Types and working principle of comparators PDF

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It contains many types of comparators and its advantages and disadvantage...

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Types of Comp N e e d f o r a co m p ar a to r 

A comparator is used in mass production to inspect the components to close tolerance with a high

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Use of line standards such as vernier caliper and micrometer required considerable skill

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Many dimensions can be checked in a very short time.

Cl a ss i f ic a ti o n o f C o m p ar a t or s

1. Mechanical Comparator: It works on gears pinions, linkages, levers, springs, etc. 2. Pneumatic Comparator: Pneumatic comparator works by using high-pressure air, valves, b 3. Optical Comparator: Optical comparator works by using lens, mirrors, light source, etc. 4. Electrical Comparator:

Works by using step up, step down transformers.

5. Electronic Comparator:It works by using an amplifier, digital signal, etc. 6. Combined Comparator: The combination of any two of the above types can give the best r Ty p e s O f C o m p a r a t o r s :

1. Mechanical compar comparators ators 

Dial Indicator

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Reed Type comparator

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Sigma Comparator

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Johansson Mikrokator

2. Optical Compar Comparators ators 

Optical Lever(Mechanical-Optical comparator)

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Zeiss Optimeter

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Zeiss Ultra Optimeter

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Zeiss Optotest Comparators

3. Electrical and Ele Electronics ctronics Compar Comparators ators 4. Pneumatic Co Compara mpara mparators tors 5) Fluid Displacement Co Compara mpara mparators tors 6) Projection Compar Comparators ators 7) Multi check Compar Comparators ators 8) Automatic Gau Gauging ging 9) Electro-Me Electro-Mechanical chanical Compara Comparators tors 10) High Sensitive Cal Calibration ibration C Compara ompara omparators tors 

Brookes Level Comparators

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Eden-Rolt Millionth Comparators

Ch ar ac t er i st i cs o f G o o d C o m p ar at or s : 1. It should be compact.

13. It should have a hard contact point, with long life. 14. It should be free from backlash and wear.

Mechanical Comparators Mechanical Comparators are the type of comparator which is made up of mechanical me levers, gears, racks and pinion, such kind of means are used to magnify the movement of mean the instrument.Magnification is nothing but multiply the small movement of the spindle/ P

this movement on to a large scale, consisting a number of divisions( Example a dial) There are four types of mechanical comparators available. 1. 2. 3. 4.

Dial Indicator Johansson Mikrokator Reed type Mechanical Comparator Sigma Comparator

Dial Indicator:

Working Of Dial Indicator It operates on the principle, that a very slight upward pressure on the spindle at the contact system of gears and levers. It is indicated on the face of the dial by a dial finger. Dial indicat round graduated dial and a contact point connected with a spiral or gear train so that hand o amount of movement of the contact point. They are designed for use on a wide range of standa dial box gauges, portal dial, hand gauges, dial depth gauges, diameter gauges and dial indicator Corresponds to a spindle movement of 1 mm. The movement mechanism of the instrument is protection. The large dial scale is graduated into 100 divisions. The indicator is set to zer representing the basic size of the part.

J O H A N S S O N “ M I K R O K AT ATO OR:

 This will cause the pointer to rotate by an amount proportional to the change  Magnification of the instrument depends upon the length, width, and a numbe strip. It can vary by changing the length of the strip with screws provided on adjust

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S I G M A C O M PA R AT ATO O R:

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This is a mechanical comparator providing magnification in 300 to5000.

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It consists of a plunger mounted on two steel strings (slit diaphragms). This linear movement for the plunger.

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The plunger carries a knife-edge, which bears upon the face of the moving b

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The cross-strip hinge is formed by pieces of flat steel springs arrange at right efficient pivot for smaller angular movements.

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The moving block carries light metal Y-forked arms. A thin phosphor bronze r ends of the forked arms and wrapped around a small drum, mounted on a sp

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Any vertical displacement of measuring plunger and hence that of the knife-e block of the cross-strip hinge to pivot.

 This causes the rotation of the Y-arms. The metallic band attached to the arm and hence the pointer to rotate.  The ratio of the effective length (L) of the arm and the distance (X) of the kn gives the first stage magnification  The ratio of pointer length (R) and radius r of the driving drum gives second instrument.

Reed type Mechanical Comparator Reed is a Long supporting rod/Shaft. In Reed type mechanical comparat Reeds to avoid frictional contacts. See the following image of a Reed type m We use four reeds, two blocks, a pointer, scale(dial) and a Plunger(Spindle) Out of four reeds, two were placed vertically(D) and two placed horizontally blocks( A and B). Here ‘A’ block is fixed block, whereas ‘B’ block is floating Block. Out of the two vertical reeds Left vertical is Fixed and the right vertical is m to the block ‘B’ Observe the Gif. that will make sense how it is exactly working.

Ad van ta g e s o f M e ch an i ca l C o 

They are cheaper compa

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Do not require electricity the outside sources do n

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They have a linear scale

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It is suitable for ordinary portable.

D i s ad van t ag e s o f M e ch a n ic a l

Wor k i n g p ri nc i p l e of O p t i c a l c om p ara t or s : The operating principle of this type, of the comparator, is based on the laws of light re The magnification system depends on the tilting of a mirror, deflects a beam of light, lever. Pr i nc i p l e o f t h e o p t i c al l e ve r If a beam of light AC is directed on to a mirror as shown in the figure, it will be reflect a dot.The angle Ɵ at which the beam strikes the mirror is equal to the angle Ɵ at whi from the mirror. When the plunger moves upwards vertically, causing the mirror to tilt in the figure.

Ze i s s u l t r a - O p t i m e t e r  The optical system of this instrument involves a double reflection of light and of magnification.  A lamp sends light rays through the green filter to filter all rays except green fatigue to the eye.  The green light then passes through a condenser which via an index mark pro mirror M1. It is then reflected to another fixed mirror M2 and back again to th  The objective lens brings the reflected beam from the movable mirror to a foc graticule containing a precise scale that is viewed by eye-piece.  The projected image of the index line on the graticule can be adjusted by me set the initial zero reading.  When correctly adjusted, the image of the index line is seen against that of th  The end of the contact plunger rests against the other end of the first movab vertical movement of the plunger will tilt the mirror.  This causes a shift in the position of the reflected index line on the eyepiece g turn measures the displacement of the plunger.

Ad van t ag e s o f op t ic a l co m p a ra to r s : 

Optical comparators have few moving linkages and hence are not subjected to friction, wear, and t

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High accuracy of the measurement.

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The magnification is usually high.

D i s a d va nt ag e s o f op t ic a l co m p ara to r s 

An electrical supply is necessary to operate these types of comparators.

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The size of these comparators are highly, and costly.

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Since the scale is projected on a screen, it is essential to use these instruments in a dark room in

Mechanical-Optical Comparators Mechanical-Optical Comparators are same as the Optical comparators but the Plunger in comparator will be replaced with the Pivoted levers.

Working Principle of Mechanical-Optical Comparato 1. The lever acts as the plunger. 2. The mirror is connected to the lever mechanism. 3. The lever is held by the pivot point. 4. The lengths L1 and L2 make the Magnification The L2 should be greater than the L1 achieved. 5. When the measuring tip is contacted the workpiece, then the lever starts rotates ab 6. The mirror will tilts accordingly about the Pivot point. 7. The reflected ray will be projected on the graduated scale and shown as the reading

Advantages of Optical Comparators 1 High accuracy will be achieved since it is having very less moving parts

P n e u m a t i c C o m p a ra t o r s :   

These instruments utilize the variations in the air pressure or velocity as an amplifying medium. A jet or jets of air are applied to the surface being measured and the variations in the backpressur variations in loused to amplify the output signals. Based on the physical phenomena, the pneumatic comparators are classified into two types. Flow or velocity type Backpressure type.

S o l e x Pn e u m a t i c Co m pa ra t o r:  This instrument was first commercially introduced by Solex Air. Gauges Ltd. It for the indication of backpressure.  It consists of a vertical metal cylinder filled with water up to a certain level an into it up to a depth corresponding to the air pressure required.

 A calibrated manometer tube is connected between the cylinder and control o  The pressure of the air supplied is higher than the desired pressure, some air bottom of the dip tube and air moving to the control volume will be at the de  The constant pressure air then passes through the control orifice and escapes  When there is no restriction to the escape of air, the level of water in the man with that in the cylinder.  But, if there is a restriction to the escape of air through the jets, back pressur circuit and level of water in the manometer tube will fall.  The restriction to the escape of air depends upon the variations in the dimens  Thus the variations in the dimensions to be measured are converted into corre variations, which can be read from the calibrated scale provided with the man

Ad v a n ta g e s o f Pn e u m a t i c Co m pa ra t o r s : 1. 2. 3. 4. 5.

A high degree of magnification is possible. No wear takes place on the workpiece due to no contact of the comparat High accuracy can be achieved due to very few moving parts. Suitable to measure the diameter of holes. The best instrument to determine the ovality and taper of the circular hol

Di s a d va n ta g e s o f p n e u m a t i c c o m pa ra t o r s : 1. 2. 3. 4.

Scale is generally not uniform Requires compressor and accurate pressure regulator Nonportable Less sensitivity

El e c t ri c a l c o m pa ra to r Working principle of Electrical compar comparators: ators: These instruments are based on the theory of Wheatstone A.C. Bridge. When the bridge is electrical flow through the galvanometer connected to the bridge, and the pointer will not deflect. Any upset will produce unbalance and cause deflection of the pointer. Electrical comparators are also called as systems.This is because they use an electro-mechanical device that converts mechanical displaceme An armature is supported on the thin steel strip and is placed in between the two coils A diagram)

Now the Armature will be unbalanced and the electric current will be passing thru it. It w deflection with the help of galvanometer. Very high magnification possible with these electrical comparators.

A d van t ag e o f e l e c t r i c al c om p arat o r 

A small number of moving parts.

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Possible to have very high magnification.

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Used for a variety of ranges.

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Remote operation can also be done.

Th e d is ad va n t ag e o f e le c t ri c a l co m p ara to r 

Required an external agency to operate i.e., A.C .power supply. 10

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Heating coils may cause zero drift.

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More expansive than the mechanical comparator.

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Comparators in Metrology – Types, Characteristics, Diagram, Advan Written by Sachi n Thorat in Metrology and Instrumentation

Table of Contents 

Introduction to Comparator : o Principle of comparator o Definition of Comparators : o Need for a comparator o Classification of Comparators o Types Of Comparators : o Characteristics of Good Comparators: o Mechanical Comparators : o o

o

o

o o

o o o

 Working Principle of Mechanical comparators: JOHANSSON “MIKROKATOR: SIGMA COMPARATOR:  Advantages of Mechanical Comparators  Disadvantages of Mechanical Comparators OPTICAL COMPARATOR  Working principle of Optical comparators:  Principle of the optical lever Zeiss ultra- Optimeter  Advantages of optical comparators :  Disadvantages of optical comparators Pneumatic Comparators : Solex Pneumatic Comparator:  Advantages of Pneumatic Comparators :  Disadvantages of pneumatic comparators : Difference between Mechanical Comparator and Pneumatic Comparators Electrical comparator LVDT  Advantage of electrical comparator Th di d t f l ti l t

device is selected to obtain the desired accuracy of measurements. It is an indirect type of instrument and u dimension is less or greater, than the standard, then the difference will be shown on the dial. It gives only and standard dimension of the workpiece. To check the height of the job H2 ,with the standard job of height principle Of Comparators

Initially, the comparator is adjusted to zero on its dial with a standard job in position as shown i taken with the help of a plunger. Then the standard job is replaced by the work-piece to be checked and the reading H2 is taken. If H change in the dimension will be shown on the dial of the comparator. Thus the difference is then ma clear variation in the standard and actual job.

Definition of Comparators : In short, Compar Comparator ator is a device which (1) Picks up small vva ariations in dimensions. (2) Magnifies it. (3) Displays it by using indica indicating ting devices, by which comparison can be made with some standard vvalue. alue.

Need for a comparator 

A comparator is used in mass production to inspect the components to close tolerance with a high



Use of line standards such as vernier caliper and micrometer required considerable skill



Many dimensions can be checked in a very short time.

Classification of Comparators

1. Mechanical Comparator: It works on gears pinions, linkages, levers, springs, etc. 2. Pneumatic Comparator: Pneumatic comparator works by using high-pressure air, valves, b 3. Optical Comparator: Optical comparator works by using lens, mirrors, light source, etc. 4. Electrical Comparator:

Works by using step up, step down transformers.

5. Electronic Comparator:It works by using an amplifier, digital signal, etc. 6. Combined Comparator: The combination of any two of the above types can give the best r Types Of Comparators :

1. Mechanical compar comparators ators 

Dial Indicator

7) Multi check Compar Comparators ators 8) Automatic Gau Gauging ging 9) Electro-Me Electro-Mechanical chanical Compara Comparators tors 10) High Sensitive Cal Calibration ibration C Compara ompara omparators tors 

Brookes Level Comparators



Eden-Rolt Millionth Comparators

Characteristics of Good Comparators: 1. It should be compact. 2. It should be easy to handle. 3. It should give a quick responses or quick results. 4. It should be reliable, while in use. 5. There should be no effects of the environment on the comparator. 6. Its weight must be less. 7. It must be cheaper. 8. It must be easily available in the market. 9. It should be sensitive as per the requirement. 10. The design should be robust. 11. It should be linear in scale so that it is easy to read and get a uniform response. 12. It should have less maintenance. 13. It should have a hard contact point, with long life. 14. It should be free from backlash and wear.

Mechanical Comparators : Working Principle of Mechanical comparators: The magnification of plunger movement can be obtained mechanical means such as levers, gear and pinion a means.

JOHANSSON “MIKROKATOR: 

Johansson “Mikrokator ‟ is a mechanical comparator having a magnification of about 5000.

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It works on the principle of a button spinning on a loop of string.

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The instrument consists of a plunger, twisted thin metal strip, spring elbow, pointer, etc.

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A very light glass pointer is attached to the Centre of the twisted strip.

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The two halves of the strip from the Centre are twisted in opposite directions, so that any pull in t hence the pointer to rotate.

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Thus the vertical movement of the plunger transmitted to the metal strip through the elbow.

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Any vertical movements of the plunger make it to twist or untwist.

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This will cause the pointer to rotate by an amount proportional to the change in the length of the

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Magnification of the instrument depends upon the length, width, and a number of twists of the tw

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It can vary by changing the length of the strip with screws provided on adjustable cantilever strip.

SIGMA COMPARATOR: 

This is a mechanical comparator providing magnification in 300 to5000.



It consists of a plunger mounted on two steel strings (slit diaphragms). This provides a frictionless



The plunger carries a knife-edge, which bears upon the face of the moving block of a cross-strip h



The cross-strip hinge is formed by pieces of flat steel springs arrange at right angles and is a very movements.



The moving block carries light metal Y-forked arms. A thin phosphor bronze ribbon is fastened to t wrapped around a small drum, mounted on a spindle carrying the pointer.

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Any vertical displacement of measuring plunger and hence that of the knife-edge makes the movin pivot. Sigma compar

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This causes the rotation of the Y-arms. The metallic band attached to the arms makes the driving rotate.

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The ratio of the effective length (L) of the arm and the distance (X) of the knife edge from the piv magnification

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The ratio of pointer length (R) and radius r of the driving drum gives second stage magnification o

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The total magnification of the instrument is thus (L/X× R/r).

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The magnification of the instrument can be varied by changing the distance (X) of knife-edge by t

There are no pure optical comparators but the instruments classed as optical comparators obtain lar instruments contributes principles through mechanical magnification All-optical comparators are capable of giving a high degree of measuring precision. Working principle of Optical comparators: The operating principle of this type, of the comparator, is based on the laws of light reflection and re system depends on the tilting of a mirror, deflects a beam of light, thus providing an optica...